These days, the problem of global warming has attracted considerable attention, and controlling emissions of carbon dioxide gas, which is one of greenhouse gases, and reducing carbon dioxide concentration in the atmosphere by fixing carbon dioxide are big challenges.
Under these circumstances, using fossil fuels containing fixed carbon dioxide as energy leads to a release of the fixed carbon dioxide into the atmosphere once again, which causes an environmental problem. In addition, since fossil fuels are a finite resource, there is a problem of depletion.
In order to solve the above problems, a fuel source other than fossil fuels is required, and expectations for development of biofuels derived from higher plants and algae have increased.
As a higher plant that is a candidate for a biofuel source, soybean, corn, palm and the like have been known. Using an edible crop as a source causes a problem with concern over food shortages. Meanwhile, while production from inedible plants such as Jatropha and Camelina has also been developed, it has a problem that the production volume per unit area is small.
Meanwhile, photosynthetic microorganisms and protozoan widely living in ponds and marsh have photosynthetic capacity as same as plants, and carbohydrate and lipid are biosynthesized from water and carbon dioxide, and accumulated in cells in several tens % by mass. It has been known that the production volume is larger than that derived from a plant, and is 10 times larger or more of that derived from a palm that is considered to have high production volume of carbohydrate and lipid, per unit area.
Incidentally, a microalga euglena that is one of the photosynthetic microorganisms is one group of flagellates, and includes euglena that is famous as motile algae. Most euglena have chloroplasts and produce energy through photosynthesis, and some euglena feed by phagocytosis or absorb nutrients. Euglena is a genus classified into both zoology and botany.
In zoology, the order Euglenida is in the order belonging to the subclass Phytomastigophorea, of the class Mastigophora in the division Protozoa, and is composed of three suborders, Euglenoidina, Peranemoidina, and Petalomonadoidina.
In Euglenoidina, as genera, Euglena, Trachelemonas, Strombonas, Phacus, Lepocinlis, Astasia, and Colacium are included. In botany, the order Euglenales is, of the class Euglenophyceae coextensive with the division Euglenophyta, and the genera in this order are, including euglena, the same as in animal classification table.
Euglena accumulates paramylon in the cells as carbohydrate. Paramylon is macromolecule particles obtained by polymerizing about 700 glucoses by beta-1,3-bonds.
When euglena is put under anaerobic conditions, wax ester fermentation in which paramylon, as a storage polysaccharide, is decomposed to finally produce a wax ester of a fatty acid, and a fatty alcohol is performed.
Non-Patent Document 1 describes that, after culturing euglena under light irradiation, while paramylon accumulation per cell is increased in an experimental area replaced by a nitrogen source-free medium, the content of paramylon per cell is reduced in an experimental area replaced by a nitrogen source-added medium.
Patent Document 1 describes that euglena is aerobically cultured and then put under anaerobic conditions, so as to ferment storage polysaccharide paramylon into a raw ester (wax ester).
Patent Document 2 describes a method for producing an unsaturated wax ester that is an alternative source of sperm oil used as a quality lubricant, by aerobically culturing a microalga euglena and adding an unsaturated fatty acid thereto, and then putting the culturing under anaerobic conditions, so as to ferment storage polysaccharide paramylon to transform into a wax ester.